Gravity drainage from a rotor in a centrifugal fibrous sheet former

ABSTRACT

Method and apparatus for forming a fibrous sheet in a centrifugal former and draining liquid from the rotor element. Rotation of the rotor produces centrifugal force which facilitates sheet formation on the inside of a cylindrical filter means and forces liquid against an outer cylindrical envelope. Slowing down of the rotation weakens the centrifugal force and allows liquid drainage by gravity through suitable means provided in the lower part of the rotor. A method for removing the filter means with the formed sheet thereon is provided wherein the screen is cut and deformed to allow removal from an opening in the cover of the apparatus.

United States Patent l 13,617,443

[ 72] inventors Jean-Pierre Chleq [56] References Cited Seyssins; UNITED STATES PATENTS Gaston Marie Lefebvre, Grenoble, both of 3 2 l O 24 10/ I 965 Grauss et al 162/384 X France 21 Appl. No. 880,242 FOREIGN PATENTS [22] Filed NOV. 26,1969 1,142,737 9/1957 France [45] f' A1971 Primary Examiner-S. Leon Bashore [73] Assignee Centre Technique de L Industrie des ASH-mm Tushin Canons Cellulose-s Allorneys- Liddy, Sullivan, Hart, Daniels & Baxley, Charles Fran E. Baxley, Frank M. Nolan and Thomas E. Tate [32] Priority Nov. 29, 1968 [33] France 176,066 ABSTRACT: Method and apparatus for forming a fibrous [54] GRAVITY DRAINAGE FROM A ROTOR IN A CENTRIFUGAL FIBROUS SHEET FORMER 6 Claims, 7 Drawing Figs.

[52] US. Cl 162/218, 162/384, 210/238 [51] Int. Cl D21] 7/00 [50] Field of Search 162/384,

sheet in a centrifugal former and draining liquid from the rotor element. Rotation of the rotor produces centrifugal force which facilitates sheet formation on the inside of a cylindrical filter means and forces liquid against an outer cylindrical envelope. Slowing down of the rotation weakens the centrifugal force and allows liquid drainage by gravity through suitable means provided in the lower part of the rotor. A method for removing the filter means with the formed sheet thereon is provided wherein the screen is cut and deformed to allow removal from an opening in the cover of the apparatus.

PATENTED NUV2 I97! SHEET 1 [IF 2 PATENTEU HUV2 lsn SHEET 2 OF 2 GRAVITY DRAINAGE FROM A ROTOR IN A CENTRIFUGAL FIBROUS SHEET FORMER The invention relates to a method for evacuating a fluid contained in a centrifugal former for forming a sheet of fibrous material (for example, paper) after this sheet has been formed.

Generally, the designation centrifugal former" means a machine intended to form sheets of fibrous material, such as paper, more particularly in laboratories, wherein this former consists substantially of an external, fixed, stator inside which a rotor may be rotatively driven. This rotor comprises:

a tight cylindrical outer envelope;

an inner filtering wall, concentric to this envelope;

means for projecting a fibrous suspension (for example, paper pulp) on to this wall, for example, a nozzle or a row of nozzles;

means for supplying a liquid into the rotor and means for removing this liquid.

The use of centrifugal formers of known construction may be divided into three operating phases.

During the first phase, the liquid is introduced into the rotor while the same rotates. Under the action of the centrifugal force, the liquid is applied to the outer envelope of the rotor and forms a wall which submerges the filtering wall of the rotor. Then,'the fibrous suspension is injected by a nozzle which may form part of an oscillating device in order to achieve the regular distribution of the suspension over the inside of the filtering wall. The fibrous suspension settles against the fluid screen on the filtering wall and is uniformly deposited on this wall. Excess liquid is eliminated, either by means of a suction device," or by an excess centrifuging system.

When the necessary quantity of fibrous suspension has been injected, the supply is stopped and the fluid is progressively evacuated from the rotor by a suction device, drawing off the liquid from the center of the liquid "wall." Next, the rotor is stopped and the filtering wall with the formed sheet is withdrawn.

This extraction can be made from the top of the former by removing the top cover. The sheet may also be withdrawn with the filtering wall through an opening in this cover, by providing a deformable filtering wall which enables it to pass through this orifice.

However, the use of a withdrawing suction device has certain disadvantages. The arrangementfor drawing across the suction device increase the bulk and the price of the installation and requires also very fine adjustments. Whatever the precautions taken, the asperation is usually accompanied by liquid being thrown off, causing a deterioration of the sheet and impairing the quality of its surface.

The invention has the object of eliminating these drawbacks by means of an evacuating method which uses no suction oevice. According to this method the removal of liquid is determined by slowing down the rotor which gives rise to a progressive reduction of the centrifugal force and is effected under the action of the force of gravity by suitable means provided at the lower end of the rotor. The forces of gravity acting on the liquid increase relative to the decreasing centrifugal forces and give rise to the drainage of the liquid.

This method does not require the provision of an asperation suction device and removes from the user the burden of having to start and control an evacuating device. Moreover. there occurs no throwing off of liquid which might alter the fibrous structure sheet.

Moreover, the progressive slowing down of the rotor makes it possible to maintain at the tangential speeds of the flow of the liquid lower values than those which would cause an alteration of the sheet under the effects of shearing action.

The invention also relates to an extraction method for withdrawing a sheet of fibrous structure after its formation from the rotor of the former.

The dismantling of the cover of the rotor in order to withdraw the sheet, usually takes very long and is impossible to achieve without special tools, owing to the clogging of the different elements.

The other method, which consists of withdrawing without dismantling the sheet through an opening in the cover by deforming the filtering wall has proved to be a rather delicate operation in known formers. In all known centrifugal formers, the construction of which is based on traditional centrifuges, the base of the rotor has the shape of an inverted bowl in which the end of the drive shaft is engaged and fixed. This construction impedes substantially the extraction of the filtering wall and prevents the user from deforming the same in such a manner as to prevent its deterioration from the point of view of a reutilization of this wall.

it is another object of the invention to eliminate this disadvantage. This is achieved by means of an extraction method, adapted to be used in a modified former, having a rotor with fiat base and wherein the method consists in:

applying prior to the rotation of the rotor an auxiliary flexible filtering support (for example, a metal sheet) against the inner surface of the filtering wall, wherein the side edges of this auxiliary support abut on each other along the generatrices of the said filtering wall;

forming in a conventional manner a sheet with fibrous structure on this auxiliary support;

cutting, after the formation of the sheet and the stopping of the rotor, this sheet along a generatrix near the adjacent edges of the auxiliary support;

deforming the auxiliary support with the sheet temporarily so as to enable it to pass through a hole provided in the cover of the former;

extracting the support and the sheet through this hole.

This method makes possible the easy and quick extraction of the sheet on its flexible support. Since the deformations of the support are not permanent the same can be used again after the sheet has been detached from its surface.

The operation of cutting the sheet of paper along one of its generatrices may conveniently be effected by pulling apart the originally abutting edges of the auxiliary support.

Preferably, the temporary deformation of the auxiliary support consists in lightly rolling up this support on itself.

The invention also relates to the rotor of a centrifugal former adapted to apply the method hereinbefore described. To this end the rotor has a flat base which is butt-mounted on a drive shaft.

This construction which differs from the construction of conventional rotors with bases in the shape of an inverted bowl, permits the easy and quick extraction of the sheet of paper after it has been formed by the method described above.

Preferably, the base of the rotor contains conduits leading between the filtering wall and the outer cylindrical shell. These conduits have the object of removing the liquid in the rotor after the formation of the sheet.

Moreover, the outer cylindrical shell may be provided with a lower lip turned towards the axis of the rotor and located near and above the base of the rotor and a similar upper lip located near the upper edge of the shell.

During the rotation the liquid thrown against the outer shell of the rotor by the centrifugal force is captured and retained between these two lips over a thickness equal to the radial depth of the lips. The two lips contribute therefore with the centrifugal force to the formation of a wall" of liquid along the outer shell with a thickness equal to the radial depth.

During the evacuation, the weakening of the centrifugal force, caused by the slowing down of the rotor, determines the discharge of liquid over the edge of the lower lip.

The radial depth of the upper and lower lips is preferably equal to the ideal thickness of the wall" of liquid desired during the rotation of the rotor.

The wall of liquid which forms during the rotation has. therefore, an optimum thickness for the formation of the sheet with fibrous structure.

Braking means may be provided for the progressive slowing down of the rotor in order to ensure tangential speeds for the discharge of the liquid at lower values than those which would produce a change in the sheet under shearing action.

The invention will be further described, by way of nonlimiting example, with reference to the accompanying drawings, in which:

FIG. 1 is an axial cross section of a centrifugal former according to the invention;

FIGS. 2a, 2b, 2c diagrams showing a former in three stages of emptying for three different speeds of the rotor;

FIGS. 30 and 3c are views in perspective of a former, showing respectively the grid fitted on the inside and during its extraction;

FIG. 3b is a detail showing the edges of the grid during their pulling apart.

A centrifugal former (FIG. 1) consists of a fixed stator l on a support 2 and a rotor comprising a tight cylindrical shell 3 and a filtering wall 4 located between an annular top cover or lip 5 and a flat base 6.

This rotor is mounted tightly on the end of a shaft 7 mounted conventionally in a roller bearing 8. The shaft is adapted to be rotated by a motor 9 and a belt 10. Reference numerals I1 and 12 indicate diagrammatically a starting device and a progressive braking device for example, a friction brake arrangement.

Moreover, the filtering wall 4 is covered by a grid 13 retained between two annular covers 14 and 15 fixed on the filtering wall 4 and adapted to be mounted at varying heights.

In addition, the tight base 6 contains conduits such as 16 which lead into the space between the shell 3 and the filtering wall 4. Underneath the base 6, an annular lip 17 retained by screws on a circular flange l8, cooperates with the upper cover 5 of equal radial depth during the rotation of the. rotor in order to permit the formation of a wall of water on the shell 3 by centrifugal action. The thickness of this wall is between the radial thickness of the lip 17 and the radial thickness of the cover 5 wherein the surplus of liquid is removed by centrifuging over the edges of this lip 17. It should be noted that the lips extend the same distance beyond the filtering wall in a direction towards an axis of the rotor and shell as determined by the shaft 7.

The stator 1 has a base 19, through which passes an evacuation conduit 20.

Finally, a nozzle 21, adapted to be driven by a reciprocating device, not shown, can inject regularly a fibrous suspension, for example paper paste, on the grid 13.

The operation of a former having the construction hereinbefore described, is as follows:

The rotor is actuated in rotation and reaches its normal rotational speed. This speed is such that the linear velocity of the filtering wall is between about 600 and 1,800 meters a minute.

Then a fluid, for example water, is introduced which, under the action of the centrifugal force, which is great relative to the force of gravity, is thrown against the shell 3 and forms a wall of water 22 (FIG. 2a). In view of the magnitude of the centrifugal force compared with the force of gravity, the inner surface of this wall of water 22 has a substantially cylindrical shape.

Next a fibrous suspension (for example, a paper paste) is injected through the nozzle 21. The suspension submerges into the film of liquid covering the grid 13 applied against the filtering wall 4 and is deposited on this grid. The excess water flows off over the edges of the lower lip 17 and off the upper cover 5.

Once the sheet has formed on the inside of the grid 13 between the end covers 14 and 15, the progressive braking device 12 is brought into action.

The centrifugal force which act on the liquid, decrease and the liquid gradually flows off under the action of the force of gravity over the edge of the lip 17 (FIGS. 2b and 2c). The braking of the rotor is achieved progressively so that the tangential speeds for the removal of the liquid remain weak enough to avoid changes in the sheet due to shearing.

This removal of liquid avoids any suction device and is achieved simply by slowing down the rotor. The final stopping, with all the water removed (FIG. 30) being achieved, the superimposed edges 23 and 24 are pulled apart which produces the opening up of the sheet 25 (FIG. 3b) along one of its generatrices.

Then the grid 13 is slightly rolled up on itself (FIG. 3c) enabling it to be extracted from the former. The sheet 25 is then detached from the grid 13 which can be'placed again into the former for further use.

It can be seen that these methods of extraction and evacuation, achieved by simple devices and limiting as far as possible the operations to be carried out by the operator require no delicate handling since the evacuation is produced by slowing down the rotor and the extraction requires no dismantling.

It should be noted that this description is not limited to the embodiment shown and that the invention comprises all variations and improvements obvious to the expert. For example, the grid 13 may have zones of different nature or dimensions, for producing a sheet with certain structural particularities (for example, filigrane).

We claim: 1. A method for forming a fibrous sheet in the rotor of a centrifugal former equipped with a cylindrical filtering wall comprising:

applying, prior to the rotation of the rotor, a flexible, filtering support against the inner surface of the filtering wall;

abutting the longitudinal side edges of said support against each other along one of the generatrices of the said filtering wall; forming a fibrous sheet on the inside of said support; cutting, after the formation of the sheet and after the stopping of the rotor, the sheet along one of its generatrices near the abutting edges of said support;

temporarily deforming said support with the sheet for reducing its diameter;

and passing said support with the sheet through an opening in the cover of the former.

2. A method as claimed in claim I wherein the cutting of the paper sheet along one of its generatrices is accomplished by pulling apart the originally abutting edges of the support.

3. A method as claimed in claim I wherein temporary deformation of the support consists in slightly rolling up the support on itself.

4. A method for draining a liquid contained in a rotor of a centrifugal former in which a fibrous sheet is formed, the rotor including a cylindrical outer envelope and a cylindrical inner filtering means, the rotor being vertically oriented, the steps comprising: rotating said rotor to maintain the liquid against said outer envelope by centrifugal force while simultaneously forming a fibrous sheet on the inside of said filtering means,

slowing down the rotation of said rotor thereby causing a progressive weakening of the centrifugal force acting on said liquid and which thereby causes a progressive increase in the relative force of gravity on said liquid, and draining said liquid through means in the lower portion of said rotor under the influence of said increased gravitational force.

5. A rotor for a centrifugal former comprising:

a cylindrical outer shell, a perforated base connected to said cylindrical outer shell and connected to a drive shaft which rotates the rotor along the axis of the cylindrical outer shell, annular lips connected to said cylindrical outer shell, said lips extending from the upper and lower ends of said shell towards said axis of said shell, the said lower lip being connected to said shell at a point below said perforated base, a cylindrical filtering wall arranged inside said shell between said upper lip and said perforated base being concentric to said shell, said lips extending the same distance beyond said filtering wall in a direction towards said axis of said shell, said rotor also including;

an auxiliary detachable filtering element arranged inside the filtering wall and in contact therewith, said element being deformable in order to be withdrawn or placed in position after defonnation; and braking means connected to said drive shaft for progressively slowing down the rotation of the rotor. 6. A rotor for a centrifugal former as claimed in claim 5, 5 wherein the base of the cylindrical shell is flat.

i II II i i 

2. A method as claimed in claim 1 wherein the cutting of the paper sheet along one of its generatrices is accomplished by pulling apart the originally abutting edges of the support.
 3. A method as claimed in claim 1 wherein temporary deformation of the support consists in slightly rolling up the support on itself.
 4. A method for draining a liquid contained in a rotor of a centrifugal former in which a fibrous sheet is formed, the rotor including a cylindrical outer envelope and a cylindrical inner filtering means, the rotor being vertically oriented, the steps comprising: rotating said rotor to maintain thE liquid against said outer envelope by centrifugal force while simultaneously forming a fibrous sheet on the inside of said filtering means, slowing down the rotation of said rotor thereby causing a progressive weakening of the centrifugal force acting on said liquid and which thereby causes a progressive increase in the relative force of gravity on said liquid, and draining said liquid through means in the lower portion of said rotor under the influence of said increased gravitational force.
 5. A rotor for a centrifugal former comprising: a cylindrical outer shell, a perforated base connected to said cylindrical outer shell and connected to a drive shaft which rotates the rotor along the axis of the cylindrical outer shell, annular lips connected to said cylindrical outer shell, said lips extending from the upper and lower ends of said shell towards said axis of said shell, the said lower lip being connected to said shell at a point below said perforated base, a cylindrical filtering wall arranged inside said shell between said upper lip and said perforated base being concentric to said shell, said lips extending the same distance beyond said filtering wall in a direction towards said axis of said shell, said rotor also including; an auxiliary detachable filtering element arranged inside the filtering wall and in contact therewith, said element being deformable in order to be withdrawn or placed in position after deformation; and braking means connected to said drive shaft for progressively slowing down the rotation of the rotor.
 6. A rotor for a centrifugal former as claimed in claim 5, wherein the base of the cylindrical shell is flat. 